basics of concrete pavement thickness design - pe civil...

Basics of Concrete Pavement Thickness Design

Concrete Pavement Design

• Geometrics• Thickness(es)• Joints

• Materials



• Materials

Most Often Influence Cost& Selection of Projects

COST



• Materials

Most Often InfluenceReal-world Performance

PERFORMANCE


Performance FactorDesign Area

Blow-upsRandom crackingFaultingPumpingSpalls

Jointing & Subbase

Materials Selection &Proportioning

ASRD-crackingFreeze-ThawScalingSkid Resistance

Thickness (Slab) Fatigue Cracking

Principles of Design

Load stresses

Volume change stresses

Curling/Warping stresses

Jointing orReinforcing

Thickness

Thickness Design Procedures

• Empirical Design Procedures• Based on observed performance

• AASHO Road Test

• Mechanistic Design Procedures• Based on mathematically calculated pavement

responses• PCA Design Procedure (PCAPAV)

PAVEMENT DESIGN

NCHRP 1-26 Phase II Final Report

Pavement design is an a priori process.The new pavement will be built in the future, on subgrades often not yet exposed or accessible; using materials not yet manufactured from sources not yet identified; by a contractor who submitted the successful "low dollar" bid, employing unidentified personnel and procedures under climatic conditions that are frequently less than ideal.

• Thickness Design Considerations:• Traffic Loads and Traffic Growth

• Subgrade and Subbases

• Drainage

• Concrete Properties

• Load Transfer

• Reliability

Design of Concrete Pavements

AASHTO Design Procedures

AASHTO Guide for Design of Pavement Structures - 1993

AASHO Road Test(1958-1960)

• Third Large Scale Road Test• Maryland Road Test (1950-51)

Rigid Pavements Only

• WASHO Road Test (1952-54)Flexible Pavements only

• Include both Rigid and Flexible Designs

• Include a wide range of axle loads and pavement cross-sections

AASHO Test Layout

AASHO Test Layout

368 rigid test sections 468 flexible test sections

Max Single Axle

Max Tandem Axle

AASHO Test Traffic

AASHO Road Test PerformanceSurviving Sections

Loop 3

1.0

2.0

3.0

4.0

5.0

0 250 500 750 1000 1250

Ser

vice

abili

ty

Concrete (36 Sect)

Asphalt (4 Sect)

Loop 4

1.0

2.0

3.0

4.0

5.0

0 250 500 750 1000 1250Load Applications

Ser

vice

abili

ty

Loop 5

1.0

2.0

3.0

4.0

5.0

0 250 500 750 1000 1250

Ser

vice

abili

ty

Loop 6

1.0

2.0

3.0

4.0

5.0

0 250 500 750 1000 1250Load Applications

Ser

vice

abili

ty

Concrete (38 Sect)

Asphalt (10 Sect)

Concrete (39 Sect)

Asphalt (11 Sect)

Concrete (47 Sect)

Asphalt (17 Sect)

AASHTO Design Procedures & Changes

1961-62 AASHO Interim Guide for the Design of Rigid and Flexible Pavements

1972 AASHTO Interim Guide for the Design of Pavement Structures - 1972

1981 Revised Chapter III on Portland Cement Concrete Pavement Design

1986 Guide for the Design of Pavement Structures1993 Revised Overlay Design Procedures1998 Revised Portland Cement Concrete Pavement Design

Log(ESALs) Z * s + 7.35*Log(D +1) - 0.06R o=

( )

+Log

PSI4.5 - 1.5

1+1.624*10

D

7

+

∆

18 46.

Standard Normal Deviate

OverallStandard Deviation

Depth

( )+ 4.22 - 0.32pt *[ ]

( )

LogS' C D 1.132

215.63* J * D -18.42

E / k

c d0.75

0.75

c

−

0 25.

* *

Change in Serviceability

Terminal Serviceability

DrainageCoefficient

Load Transfer

Modulus ofRupture

Modulus of Elasticity

Modulus ofSubgrade Reaction

1986-93 Rigid Pavement Design Equation

AASHTO DESIGN Traffic

ESAL’s or E-18’s The number and weight of all axle loads from the anticipated vehicles expected during the pavement design life - expressed in 18-kip (80 kN) Equivalent Single Axle Loads for each type of pavement.

—Rigid ESAL’s or E-18’s

—Flexible ESAL’s or E-18’s

AASHTO DESIGN Traffic - ESALs

Equivalent Number of 18k Single Axle Loads

ESALs GENERATED BY DIFFERENT VEHICLES/DAY

VEHICLE NUMBER RIGIDESALs

FLEXIBLEESALs

Single Units 2 Axle 20 6.38 6.11Busses 5 13.55 8.73Panel Trucks 10 10.89 11.11Semi-tractor Trailer 3 Axles 10 20.06 13.41Semi-tractor Trailer 4 Axles 15 39.43 29.88Semi-tractor Trailer 5 Axles 15 57.33 36.87Automobile, Pickup, Van 425 1.88 2.25

Total 500 149.52 108.36

AASHTO DESIGNTraffic

Load Equivalence Factor (LEF) The Ratio of the Effect (Damage) of a Specific Axle Load on Pavement Serviceability to the Effect Produced by an 18-kip Axle Load at the AASHO Road Test.

Change for each: Pavement TypeThicknessTerminal Serviceability.

AASHTO DESIGNTraffic

Load Equivalence Factor (LEF)

No. of repetitions of 18-k SAL Load causing given ∆PSI No. of repetitions of X-k Y-Axle Load for a same ∆PSI

Change for each: Pavement TypeThicknessTerminal Serviceability.

For a Given Stress or Strain:

LOAD EQUIVALENCY FACTORSFOR A GIVEN PAVEMENT STRUCTURE

Stress or Strain of X-kip Load on Axle Type Y

Stress or Strain of 18-kip Load on a Single Axle

For a Given Serviceability Loss:

LOAD EQUIVALENCY FACTORSFOR A GIVEN PAVEMENT STRUCTURE

# of Repetitions of X-kip Load on Axle Type Y

# of Repetitions of 18-kip Load on a Single Axle

PSI PSI

ConcreteResponse

AsphaltResponse

Since pavement responses are different, the equivalency factors (LEFs) are different. When multiplying the traffic by the different equivalencies, you get different ESALs

AASHTO DESIGN Traffic

Subgrade and Subbases

• Subbase• Layer of material

directly below the concrete pavement.

• Subgrade• Natural ground, graded,

and compacted on which the pavement is built.

Subbase

Subgrade

Concrete Section

Subgrade / Subbase Strength

Modulus of Subgrade Reaction, k

Reaction

Stacked Plates

Hydraulic Jack Pressure Gauge

Deflection Dial at 1/3 Points

k (psi/in) = unit load on plate / plate deflection

Subgrade and SubbasesDesign

• Subgrade strength is not a critical element in the thickness design.

• Has little impact on thickness.

• Need to know if pavement is on:• Subgrade (k ≈ 100 psi/in.),

• Granular subbase (k ≈ 150 psi/in.),

• Asphalt treated subbase (k ≈ 300 psi/in.)

• Cement treated/lean concrete subbase (k ≈ 500 psi/in.).

AASHTO DESIGNSubgrade Strength

Typical Soil Relationships

Soil Type Strength k-value(psi / in.)

Mr (psi) CBR

Silts / Clays Very Low 50-100 1000-1900 <3

Fine grained Low 100-150 1900-2900 3-5.5

Sands Medium 150-220 2900-4300 5.5-12

Gravely soils High 220-250 4300-4850 >12

Bitumin.Treat. High 350-450 100,000+ >12

Cement.Treat./LCB High 400-600 500,000+ >12

Subgrade and SubbasesPerformance

• Proper design and construction are absolutely necessary if the pavement is to perform.

• Must be uniform throughout pavement’s life.

• Poor subgrade/subbase preparation can not be overcome with thickness.

• Any concrete pavement, built of any thickness, will have problems on a poorly designed and constructed subgrade or subbase.

UNIFORMITY:

The Key To

GOOD PAVEMENT

PERFORMANCE

Design for Uniform Support

• Expansive soils

• Frost susceptible soils

• Pumping (loss of Support)

• Cut-fill transitions

• Poorly compacted excavations• Utility work• Culverts

Sources of Non-Uniform Support

PAVEMENT DESIGNSubbase Effects

The current Design does not model the contribution of bases accurately.

At the AASHO Road Test, it was found that the concrete pavements with granular bases could carry about 30% more traffic.

The current design procedures allows concrete pavements built with granular bases to carry about 5 - 8% more traffic.

Flexural Strength (S’c) Determination

Head of Testing Machine

L/3

Span Length = L

d=L/3

Span Length = L

L/2

Third-point Loading Center-point Loading

Concrete Properties

Concrete Properties

f’c = Compressive Strength (psi)S’c = Flexural Strength (psi)

S’c = 8-10 √ √ f’c


Cylinder Depth

Compressive Strength f’c

Concrete Properties

Use average, in-field strength for design

(not minimum specified)

If specify minimum flexural strength at 28-day of 550 psi & allow 10% of beams to fall below minimum:

STEP 1Estimate SDEV:9% for typical ready mix.SDEV = 550 * 0.09 = 50 psi

STEP 2S’c design = S’c minimum + z * SDEV

S’c design = 550 + 1.282 * 50S’c design = 614 psi

Drainage

Conditions for Pumping• Subgrade Soil that will go

into Suspension

• Free water between Slab and Subgrade

• Frequent Heavy wheels loads / Large Deflections

Drainage

• Major Conclusions• For Doweled PCC

Pavements, Drainage has little affect on Faulting

• Does reduce D-cracking

• Drainage significantly reduces fatigue cracking and rutting in AC Pavements

• Day lighted drainage works best with permeable bases

NCHRP 1-34: Subsurface Drainage for Pavements

Load Transfer

• A slabs ability to share its load with neighboring slabs

• Dowels

• Aggregate Interlock

• Concrete Shoulders• Tied Concrete, curb & gutter,

and extended lane have same effect.

L= x

U= 0

Poor Load Transfer

Load Transfer

Good Load Transfer

L= x/2 U = x/2

Aggregate Interlock

Shear between aggregate particlesbelow the initial saw cut

Aggregate Interlock

Dowel bars

• Lengths from 15-18 in.

• 6.0 in. min. embedment length

• Diameter• 1.25 - 1.50 in. for roads

• 1.5 - 2.0 in. for airports

• Epoxy or other coating used in harsher climates for corrosion protection

Deflections in Concrete Pavement

12 ft Lanes

Outside Pavement Edge (free edge)

Longitudinal Centerline(acts as tied concrete shoulder)

Undoweled transverse Joint Doweled transverse Joint

2 Di

~2.5 Di5 Di

~3.5 Di

Di Di

Load Transfer

AASHTO DESIGN

Effect of Dowels and Shoulders

0.0E+00

1.0E+07

2.0E+07

3.0E+07

4.0E+07

7 8 9 10 11 12Thickness

Allo

wab

le E

SA

Ls

Dowels & Shoulders

Dowels & No Shoulders

No Dowels & Shoulders

No Dowels & No Shoulders


• Exclude dowels if:• Slab thickness < 7.0 in

• Include dowels if:• Slab thickness > 8.0 in.

TrucksControl

Thickness

To Dowel or Not to Dowel?

AASHTO DESIGNReliability

The statistical factors that influence pavement performance are:

• RELIABILITY, R • The statistical probability that a pavement will meet

its design life.

• STANDARD DEVIATION, so• The amount of statistical error present in the design

equations resulting from variability in materials, construction, traffic, etc.


Log ESALs

SE

RV

ICE

AB

ILIT

Y

pt

po

Design Curve

PerformanceCurve

ZR * so

WinPAS

PCAPAV Design Procedure

• Mechanistic stress analysis

• Calibrated to field tests, test roads

• Control criteria can be either:• Fatigue (cracking)• Erosion (pumping)

• Available computer program (PCAPAV)

Design Basics

Fatigue

• Midslab loading away from transverse joint produces critical edge stresses

Erosion

• Corner loading produces critical pavement deflections

Transverse joint Transverse joint

Critical Loading Positions

Differences Between Design Procedures

• Traffic Classification:• AASHTO - uses 18-kip ESALs

• PCA - uses axle load distribution

• Reliability• AASHTO - Reliability

• PCA - Load Safety Factors

• Drainage

PCAPAV Design

• Fatigue • Keeps pavement stresses due to repeated loads within

safe limits

• Erosion• Limits the effects of pavement deflections at edges,

joints and corners.

Two design criteria:


• Concrete Properties• Flexural strength (modulus of rupture)

• Subgrade Strength, or subgrade-subbase combination• modulus of subgrade reaction, k-value

• Weights, frequencies, and types of truck axle loads

• Load Transfer

• Load Safety Factor

• Design Period

Design Factors

PCAPAV Design Traffic

• Numbers & weights of heavy axle loads expected during the design life

• ADT (average daily traffic in both directions)

• ADTT (average daily truck traffic in both directions)• Includes only trucks with six tires or more

• Does not include panel and pickup trucks and other four-tire vehicles.

• Axle loads of trucks

PCAPAV DesignTraffic

• Axle loads Distribution• The number of single

and tandem axles over the design period

• Expressed as Axles per 1000 trucks


Axle loadKips

Single Axles28-3026-2824-2622-2420-2218-2016-1814-1612-1410-12

Tandem Axles48-5244-4840-4436-4032-3628-3224-2820-2416-2012-16

Axles/1000Trucks

0.581.352.775.929.8321.6728.2438.8353.94168.85

1.963.9411.4834.2781.4285.54152.2390.52112.81124.69

Axles indesign period

6,31014,69030,14064,410106,900235,800307,200422,500586,900

1,837,000

21,32042,870124,900372,900885,800930,700

1,656,000984,900

1,227,0001,356,000


Light Residential

ResidentialRural & secondary rds.

Collector streetsRural & secondary rds.(heavy trucks)

Minor Arterial Sts.Primary roads

Major Arterial Sts.

3

10 - 30

50 - 500

300 - 600

700 - 1500

LR

1

2

2

3

1.0

1.0

1.1

1.2

1.2

Two-way ADTT Category LSF

Traffic Categories

PCAPAV DesignLoad Safety Factors

• Interstate, interprovincial, multilane projects• LSF = 1.2.

• Highways and arterial streets• LSF = 1.1

• Roads, residential streets, and other streets that carry small volumes of truck traffic

• LSF = 1.0

Recommended values

PCAPAV

PCAPAV DesignSimplified Procedure

• Designs presented in Tabular Form• Traffic

• Type of road• Axle-load category (for the road type)• Avg. daily truck traffic• Probable maximum truck weights

• Subgrade and Subbase• Dowels & slab edge support• Concrete strength


Foundation Support, k, MPa/m

Flexural Strength, MPa

Light Resident.

ADTT = 50100500

ADTT = 300600

ADTT = 102050

3.8 4.1 4.5 4.1 4.53.8

165165175

150150165

190200215

190190215

215225

200215

140150150

175175190

200200

150150150

175175190

200200

140140150

140140140

165175175

165165175

190190

175190

No Dowels - No edge support

40 80

ResidentialRural & Sec. Rd.

CollectorRural & sec. Rd.

Minor Arterial

2-way ADTT = 3 150 mm 140 140 140 125 125


Foundation Support, k, MPa/m

Flexural Strength, MPa

Light Resident.

ADTT = 50100500

ADTT = 300600

ADTT = 102050

3.8 4.1 4.5 4.1 4.53.8

140140150

125140140

165175175

150165175

190190

175190

125125125

160160160

165175

125125140

150150165

175175

125125125

125125125

140150150

140140150

165165

150165

No Dowels - With Edge Support

40 80

ResidentialRural & Sec. Rd.

CollectorRural & sec. Rd.

Minor Arterial

2-way ADTT = 3 125 mm 125 125 125 125 125

Typical Concrete Pavement Thickness

• Depends on traffic load, subgrade, and climate. • City streets, secondary roads, and small

airports• 100 to 175 mm (4 to 7 in.)

• Primary roads and interstate highways • 175 to 280 mm (7 to 12 in.)

• Large airports • 200 to 460 mm (8 to 18 in.)

1986-93 RIGID PAVEMENT DESIGN

Factors Affecting Rigid PavementsThicknessServiceability (po, pt) Traffic (ESALs, E-18s)Load Transfer (J)Concrete Properties (S’c, Ec)Subgrade Strength (k, LS) Drainage (Cd) Reliability (R, So)

AASHTO DESIGN Serviceability

Serviceability -the pavement’s ability to serve the type of traffic (automobiles and trucks) that use the facility

Very Good

Good

Fair

Poor

Very Poor

5.0

4.0

3.0

2.0

1.0

0.0

Present Serviceability Index (PSI)

Pre

sen

t S

ervi

ceab

ility

Ind

ex

Accumulated Traffic

po

Rehabilitation Requiredpt

PSI

AASHTO DESIGNConcrete Properties

There are two concrete properties that influence pavement performance

• Flexural Strength (Modulus of Rupture), S’c– Average 28-day strength

– 3rd-Point Loading

• Modulus of Elasticity, Ec


Flexural Strength (S’c) Determination


L/3

Span Length = L

d=L/3

Span Length = L

L/2

Third-point Loading Center-point Loading


Use average, in-field strength for design

(not minimum specified)

If specify minimum flexural strength at 28-day of 550 psi & allow 10% of beams to fall below minimum:

STEP 1Estimate SDEV:9% for typical ready mix.SDEV = 550 * 0.09 = 50 psi

STEP 2S’c design = S’c minimum + z * SDEV

S’c design = 550 + 1.282 * 50S’c design = 614 psi


Modulus of ElasticityEc = 6750 S’cEc = 57,000 (f’c)0.5

Flexural Strength Modulus of Elasticity600 psi 3,900,000 psi650 psi 4,200,000 psi700 psi 4,600,000 psi

Avenues for water entry

WATER-TABLE

Water-Table Rise

CapillarySuction fromWater-Table

Natural Drainagefrom High-Ground

From Edge VaporMovement

Surface Entry

2 4

1

3

1

5

PAVEMENT

BASE

AASHTO DESIGNDrainage , Cd


The statistical factors that influence pavement performance are:

• RELIABILITY, R - The statistical probability that a pavement will meet its design life.

• STANDARD DEVIATION, so -The amount of statistical error present in the design equations resulting from variability in materials, construction, traffic, etc.


Log ESALs

SE

RV

ICE

AB

ILIT

Y

pt

po

Design Curve

PerformanceCurve

ZR * so

WinPAS


• Mechanistic stress analysis

• Calibrated to field tests, test roads

• Control criteria can be either:

• Fatigue (cracking)• Erosion (pumping)

• Available computer program (PCAPAV)

Design Basics

Differences Between Design Procedures

• Traffic Classification:• AASHTO - uses 18-kip ESALs

• PCA - uses axle load distribution

• Reliability• AASHTO - Reliability

• PCA - Load Safety Factors

• Drainage• PCA does not include

PCAPAV Design

• Fatigue • Keeps pavement stresses due to repeated loads within

safe limits

• Erosion• Limits the effects of pavement deflections at edges,

joints and corners.

Two design criteria:

Fatigue Analysis

• Performed for edge stresses (critical stresses)

• Based on stress ratio

• Fatigue not consumed by repetitions of one load is available for repetitions of other loads.

Equivalent Flexural Stress 28-Day Modulus of RuptureSR =

Fatigue Analysis• Allowable number of load

repetitions for each axle group is determined fromnomographs

• % Fatigue is calculated for each axle group

• Total fatigue consumed should not exceed 100%.

Expected repetitionsAllowable repetitions% Fatigue =

Erosion Analysis

• Repetitions of heavy axle loads cause:• pumping; erosion of subgrade, subbase and shoulder

materials; voids under and adjacent to the slab; and faulting of pavement joints.

• Erosion is a function of Power, or rate of work.Power = corner deflection (w) * pressure (p) * area

duration of deflection.

• A thin pavement with its shorter deflection basin receives a faster load punch than a thicker slab.

Erosion Analysis

• Performed for corner deflections (critical deflections)

• Erosion factor is determined from tables

• Allowable number of load repetitions for each axle group is determined from nomographs

• Erosion Damage is calculated for each axle group% Erosion Damage = Expected repetitions

Allowable repetitions

• Total erosion damage from all axle groups should be less than 100%

PCAPAV Design

• Fatigue usually controls design of light-traffic pavements

• Single-axles usually cause more fatigue damage

• Erosion usually controls design of undoweledmedium- and heavy-traffic pavements

• Tandem-axles usually cause more erosion damage

Design controlled by:


• Selection of an adequate thickness is dependent upon the choice of other design features:• Jointing system

• Shoulder type

• Subbase type

PCAPAV Design Procedure Concrete Properties

• Flexural Strength (Modulus of Rupture),

• Avg. 28-day strength in 3rd-point loading

• Other Factors• Fatigue Properties

• Concrete Strength Gain with Age L/3

Span Length = L

d=L/3

Third-point Loading

PCAPAV DesignConcrete Properties

Comparison of f’c, MR, and Required Thickness

CompressiveStrength

3000 psi4000 psi5000 psi

Third PointFlexural Strength

450 - 550 psi510 - 630 psi570 - 710 psi

Effect on Slab Thickness

7.0 in6.5 in.6.0 in.

PCAPAV DesignSubgrade Properties

Modulus of Subgrade Reaction, k-value

Plate load on subgrade Plate deflection on subgradek =

5.0 psi 0.5 ink = = 100 psi / in.

Reaction

Stacked Plates Pressure Gauge

Subgrade

Plate-Load Test


• Plate-load test is rarely performed• time consuming & expensive

• Estimate k-value by correlation to other tests • e.g. California Bearing Ratio (CBR) or R-value tests.

• Lean concrete subbases increases k-value.


Comparison of Soil Types and k-value

k-value

100 psi/in.200 psi/in.300 psi/in.

Type of Soil

Silts and claysSandy soilsSand-gravels

Remarks

SatisfactoryGoodExcellent

Effect of Untreated Subbase on k-value

Subbase k-value

4 in.

85165235320

Subgradek-value (psi/in)

75150225300

6 in.

96180242330

9 in.

117210280367

12 in.

140243330430

Effect of Cement-treated Subbase on k-value

Subbase k-value

4 in.

220367514

Subgrade k-value (psi/in)

75150225

6 in.

294477698

9 in.

386680900

12 in.

496845--

Effect of Untreated Subbase on k-value

Subbase k-value

4 in.

85165235320

Subgradek-value (psi/in)

75150225300

6 in.

96180242330

9 in.

117210280367

12 in.

140243330430



Effect of Cement-treated Subbase on k-value

Subbase k-value

4 in.

220367514

Subgrade k-value (psi/in)

75150225

6 in.

294477698

9 in.

386680900

12 in.

496845--

PCAPAV DesignDesign Period

• 20 to 35 years is commonly used • Shorter or longer design period may be

economically justified in some cases • A special haul road to be used for only a few years.

PCAPAV Design Traffic

• Numbers & weights of heavy axle loads expected during the design life

• ADT (average daily traffic in both directions)

• ADTT (average daily truck traffic in both directions)• Includes only trucks with six tires or more


• Axle loads of trucks


• Axle loads Distribution• The number of single

and tandem axles over the design period

• Expressed as Axles per 1000 trucks


Axle loadkN

Axles/1000Trucks

Axles indesign period

Single Axles125-133115-125107-11597.8-10788.8-97.880.0-88.871.1-80.062.2-71.153.3-72.244.4-53.3

0.581.352.775.929.83

21.6728.2438.8353.94

168.85

6,31014,69030,14064,410

106,900235,800307,200422,500586,900

1,837,000Tandem Axles213-231195-213178-195160-178142-160125-142107-12588.8-10771.1-88.853.3-71.1

1.963.94

11.4834.2781.4285.54

152.2390.52

112.81124.69

21,32042,870

124,900372,900885,800930,700

1,656,000984,900

1,227,0001,356,000


Light Residential

ResidentialRural & secondary rds.

Collector streetsRural & secondary rds.(heavy trucks)

Minor Arterial Sts.Primary roads

Major Arterial Sts.

3

10 - 30

50 - 500

300 - 600

700 - 1500

LR

1

2

2

3

1.0

1.0

1.1

1.2

1.2

Two-way ADTT Category LSF

Traffic Categories

PCAPAV DesignLoad Safety Factors

• Interstate, interprovincial, multilane projects• LSF = 1.2.

• Highways and arterial streets• LSF = 1.1

• Roads, residential streets, and other streets that carry small volumes of truck traffic

• LSF = 1.0

Recommended values

PCAPAV Design Other Loads

• Warping - moisture variations.

• Creates compressive restraint stresses in the slab bottom.

• Curling - temperature variations.• During the day, the top surface is warmer than the bottom

and stresses develop at the slab bottom.

• During the night, the top is colder and stresses develop at the slab surface.

• Assumed to cancel each other out.

Warping and Curling of Concrete

PCAPAV DesignDesign Procedures

• Rigorous• Detailed axle-load-distribution data is available

• Simplified• Axle-Load Data Not Available

• Designer does not directly use the axle-load data

• Tabular form

PCAPAV DesignRigorous Procedure

• Requires the following design factors:• Type of joint and shoulder

• Concrete flexural strength (MR) at 28 days

• k-value of subgrade or subgrade-subbase combination

• Load safety factor (LSF)

• Axle-load distribution

• Expected number of axle-load repetitions

• Use PCAPAV Computer ProgramPCAPAV

Design Tip

Don’t Drinkand Design

basics of concrete pavement thickness design - pe civil...

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